Bermuda Triangle 1817 Tsunami Triggered by Quake Hit Philadelphia

A one-foot tsunami-like natural event, spurred by a large offshore earthquake in the Bermuda Triangle, struck Philadelphia nearly 200 years ago, according to the U.S. Geological Survey.

At around 4:30 a.m. ET on Jan. 8, 1817, a magnitude-7.4 earthquake shook the northern tip of the Bermuda Triangle, and a subsequent tsunami tossed ships docked along the Delaware River south of Philadelphia several hours later, according to the study in the September/October issue of the journal Seismological Research Letters.

The earthquake shook the East Coast from Maryland to Georgia, where seismic waves made the State House bell ring multiple times, according to archival accounts. (http://news.yahoo.com/bermuda-triangle-earthquake-triggered-1817-tsunami-185804359.html) Geologists of the day estimated the earthquake's magnitude was between 4.8 and 6.

Armed with new geologic equipment and computer modeling of the tsunami, U.S. Geological Survey geophysicist Susan Hough and a team of researchers say the earthquake's magnitude was 7.4, according to the study.

"That was the eureka moment," Hough told LiveScience. "Darned if that wave doesn't hit the Delaware River and slow way down."

The size and location, or epicenter, of the 1817 earthquake has never been pinned down so closely before. Newly uncovered archival records allowed Hough and her colleagues to discover where the shaking was the most powerful.

Scientists believe that the tsunami began about 800 miles south of Delaware Bay and 400-500 miles offshore of South Carolina, or on the northwestern limb of the famed Bermuda Triangle.

"When we started to say, 'OK, it's the Bermuda Triangle Fault,' that did not go over well," Hough said. "Some of our colleagues didn't want us to get into all this hooey."

The U.S. Geological Survey measures offshore earthquakes and conducts studies to gain a greater scientific understanding of faults. The 1929 magnitude-7.2 earthquake along the Grand Banks in Newfoundland started a landslide, which then led to a tsunami. Waves up to 13 feet high struck the coast, killing 29 people. About 10,000 were left without homes.

On March 11, 2011, an earthquake off the Pacific coast of Tohoku, about 43 miles east of the Oshika Peninsula, created a tsunami. It was the most powerful known earthquake to have struck Japan, and the fifth most powerful in the world since record-keeping began in 1900.